Indirect heat exchangers allow the transfer of heat energy between different mediums, whilst avoiding direct contact or mixing there-between. Either or both medium may comprise a heat transfer fluid, in which event it is common that a flow conduit such as a tube is arranged to promote heat transfer to/from the fluid over a length of the conduit.
For a number of heat exchange applications, particularly for which there are spatial constraints of the size of a heat exchanger, helical conduits may be used. Within a helical tubular heat exchanger arrangement, one or more tubes may make multiple turns about a common axis so as to provide a relatively long flow path within a relatively small volume and thereby provide a greater capacity for heat exchange than, for example a straight tube heat exchanger.
Whilst the strength of the fluid conduits may be sufficient to maintain a desired helical configuration, in use, heat exchangers experience thermal loading which can lead to fatigue over time and, accordingly, it is common to provide a support structure for the tubes. Depending on the particular application of the heat exchanger, flow-induced vibration in the tubes and/or machine induced vibration may also need to be accounted for.
A conventional support arrangement for a helical tube heat exchanger comprises a number of linear support bars at suitable locations, angularly spaced about the central axis of the helix. The bars extend in the direction of the axis (i.e. perpendicular to the direction of the tubes) and have a plurality of recesses along their length spaced to receive adjacent turns of the tubes. There are a number of problems with such an arrangement. The correct alignment of the support bars and tubes can be awkward to assemble, particularly for large/complex tube bundles. For some tube arrangements, such as an arrangement in which alternate adjacent tubes are wound in opposing directions, these problems are exacerbated and the support bar itself can be complicated and costly to manufacture.
Furthermore a bar with predetermined tube fixation points cannot accommodate variations in design and thus accepts only a fixed tube pitch and spacing. The linear supports may provide a thermal inertia which does not contribute to the heat exchanger efficiency and, particularly for thicker supports that are required to bear a large tube bundle of tubes, may adversely affect heat exchanger performance, e.g. by insulating the tube and/or prescribing a non-optimal tube spacing.
Thermal loading of the heat exchange tubes may remain a problem in a conventionally supported system due to thermal loading of the tubes relative to the discrete linear supports. A support that is optimised for strength will typically offer different thermal expansion properties to a tube and may experience different loading at its opposing ends due to its orientation relative to the tube bundle.